There is a known endoscope that has a wide angle of view of 180° or more and that can simultaneously observe front, lateral, and rear fields of view (for example, see PTL 1). In the endoscope of PTL 1, for example, when the endoscope, which has an angle of view of 180° or more, is used in the large intestine, which has a number of folds, it is possible to observe the rear sides of the folds without significantly changing the direction of a distal end of the endoscope, thus facilitating the operation performed by a user, and to reliably find a lesion. An illumination device of this endoscope diffusely emits illumination light guided by a light guide, by using a diffusion layer, thereby making it possible to uniformly illuminate a wide range, including a lateral area and a forward area.